Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 280417
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
817 PM PST TUE JAN 27 2015

.DISCUSSION...THE FORECAST WAS UPDATED TO EXTEND THE AIR STAGNATION
ADVISORY IN SOUTHERN OREGON VALLEYS BY 24 HOURS...THROUGH SATURDAY
MORNING. THIS CHANGE IS DUE TO VERY GOOD MODEL AGREEMENT THAT HIGH
PRESSURE ALOFT WILL STRENGTHEN OVER OUR AREA AT THE END OF THE
WEEK.

THE STRATUS IN THE UMPQUA VALLEY DID FINALLY BREAK UP WITHIN THE
PAST COUPLE HOURS. THIS IS INDICATIVE OF THE TEMPORARY CHANGE IN
THE VERTICAL TEMPERATURE PROFILE WITH COOLING ALOFT AS A WEAK
FRONT HAS REACHED THE COAST AND WILL DISSIPATE OVERNIGHT. VALLEY
INVERSIONS WILL DEVELOP AGAIN LATE TONIGHT BUT WILL BE THE WEAKEST
THEY HAVE BEEN IN OVER A WEEK...SINCE LAST TUESDAY MORNING. THE
VALLEY INVERSIONS WILL BE JUST A BIT STRONGER WEDNESDAY NIGHT AND
THEN MUCH MORE NOTICEABLY SO AS THE NEXT RIDGE BUILDS TO THE WEST
COAST THURSDAY NIGHT INTO FRIDAY MORNING. HIGH PRESSURE WILL
PERSIST THROUGH SATURDAY AND POSSIBLY INTO SUNDAY.

THE 18Z GFS AND 12Z ECMWF HAVE SIGNIFICANT DIFFERENCES IN THE LONG
TERM, BUT BOTH DO INDICATE A COLD FRONT WILL HOLD TOGETHER AND
MOVE ACROSS OUR AREA EARLY NEXT WEEK WITH THE POSSIBILITY OF THE
FIRST PERIOD OF WIDESPREAD RAIN IN OUR AREA SINCE JANUARY 17TH/18TH.
THE VERY EARLY INDICATION IS THAT SNOW LEVELS WOULD BE IN THE
RANGE OF 5500 TO 7000 FEET.

&&

.AVIATION...BASED ON THE 28/00Z TAF CYCLE...ALONG THE COAST...THE
LOWER CONDITIONS WILL RETURN TO THE SAME AREAS THIS EVENING WITH
MVFR CIGS FROM AROUND 03Z. INLAND...THE LOWER CONDITIONS WILL RETURN
TO THE SAME AREAS LATE TONIGHT AROUND 08Z THROUGH WEDNESDAY
MORNING...BUT COVERAGE WILL BE A BIT LESS THAN LAST NIGHT THE
REMAINDER OF THE AREA WILL REMAIN VFR THROUGH WEDNESDAY. /FB

&&

.MARINE...UPDATED AT 115 PM TUESDAY 27 JANUARY 2015...WEST SWELL
WILL GRADUALLY SUBSIDE WITH LIGHT SOUTH WINDS THROUGH WEDNESDAY. A
WEAK FRONT WILL MOVE THROUGH THE COASTAL WATERS THIS EVENING THEN
DISSIPATE WEDNESDAY. MODERATE NORTHERLY WINDS WILL DEVELOP
THURSDAY INTO FRIDAY AS OFFSHORE HIGH PRESSURE BUILDS...RESULTING
IN INCREASED CHOP. THE HIGH PRESSURE WILL WEAKEN SATURDAY NIGHT
INTO SUNDAY. /FB

&&

.PREV DISCUSSION... /ISSUED 213 PM PST TUE JAN 27 2015/

DISCUSSION...HIGH AND MID LEVEL CLOUDS ARE BLANKETING MOST OF THE
CWA AND THIS WILL PERSIST INTO TONIGHT. LOW CLOUDS ARE STILL IN
ROSEBURG AND IT MAY NOT BREAK OUT AT ALL THROUGH EARLY THIS
EVENING. A WEAK FRONT WILL MOVE INTO THE NORTHWEST PART OF THE
FORECAST AREA THIS EVENING, THEN DISSIPATE TONIGHT. THIS FRONT
WILL HAVE LITTLE OR NO IMPACT ON THE CURRENT AIR STAGNATION
ADVISORY FOR THE WESTSIDE VALLEYS AND VALLEYS EAST OF THE
CASCADES. THERE IS A CHANCE THE ATMOSPHERE WILL MIX OUT ENOUGH
EAST OF THE CASCADES THIS AFTERNOON, BUT THE INVERSION WILL
DEVELOP AGAIN TONIGHT AND PERSIST THROUGH AT LEAST SATURDAY
MORNING.

OVERALL THE PATTERN IS NOT GOING TO CHANCE MUCH WHICH MEANS MUCH
OF THE SAME WITH LOW CLOUDS AND FOG DEVELOPING IN THE EVENINGS AND
LASTING THROUGH THE MORNING HOURS FOR THE WESTSIDE VALLEYS. IT`S
POSSIBLE WE COULD HAVE SUFFICIENT CLOUD COVER TONIGHT TO DELAY OR
LIMIT THE EXTENT OF THE FOG AND LOW CLOUDS TONIGHT INTO WEDNESDAY
MORNING, BUT WE`LL LET THE NIGHT SHIFT TAKE ANOTHER LOOK AT THIS.
-PETRUCELLI

MEDIUM RANGE FORECAST...SATURDAY THROUGH TUESDAY.

THE EXTENDED FORECAST PERIOD WILL START OFF RELATIVELY WARM AND DRY
WITH A STRONG LONG WAVE RIDGE OFF THE WEST COAST.

THE RIDGE AXIS WILL MOVE ONSHORE SATURDAY NIGHT INTO SUNDAY. THIS
USUALLY OPENS UP THE STORM DOOR BUT THE UPSTREAM SYSTEMS ARE WEAK.
THOSE SYSTEMS WILL RIDE OVER THE RIDGE AND FLATTEN IT...AND FLOW
ALOFT WILL BECOME ZONAL SUNDAY INTO MONDAY.

BOTH THE EC AND GFS SOLUTIONS MOVE A FRONT ONSHORE THIS WEEKEND FOR
THE NEXT CHANCE OF PRECIPITATION OVER THE AREA. THE EC MOVES THE
FRONT ONSHORE LATE SATURDAY NIGHT INTO SUNDAY MORNING WHILE THE GFS
MOVES A WETTER FRONT ONSHORE SUNDAY EVENING. BOTH MODELS STALL
THE FRONT OVER THE AREA AS IT BECOMES PARALLEL TO THE UPPER LEVEL
FLOW...BUT THE EC DOES IT OVER DOUGLAS COUNTY WHILE THE GFS STALLS
IT OVER NORTHERN CALIFORNIA.

THE MODEL SOLUTIONS DIVERGE EVEN MORE EARLY NEXT WEEK.  THE GFS
SOLUTION HOLD ON TO A WEAK LONG WAVE RIDGE OVER THE WESTERN U.S.
WHILE THE EC REDEVELOPS THE OFFSHORE LONG WAVE RIDGE.  THE DGEX
SOLUTION IS IN BETWEEN...STARTING WITH THE GFS SOLUTION...THEN
MOVING TOWARD THE EC SOLUTION TUESDAY.  OVERALL IT LOOKS LIKE THE
FRONTAL ZONE WILL OSCILLATE BACK AND FORTH OVER THE CWA MONDAY INTO
TUESDAY AS WAVES DEVELOP AND PROPAGATE ALONG THE BOUNDARY.  THIS
WILL MAKE FOR GENERALLY UNSETTLED WEATHER WITH LIGHT TO MODERATE
INTERMITTENT PRECIPITATION.

EVENTUALLY THE OFFSHORE RIDGING WILL DRY THE AREA OUT AND WEDNESDAY
LOOKS TO BE DRY. -JRS

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL 1 PM PST SATURDAY FOR
     ORZ023-024-026-616-620-622.
     AIR STAGNATION ADVISORY UNTIL 1 PM PST SATURDAY FOR
     ORZ029>031-623>625.

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

DW/DW/FJB



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